The unprecedented decision will virtually halve the number of children selected by academic ability at three schools in the south London borough of Wandsworth, which is Conservative controlled. Parents objected to the admissions policies of the three schools, which chose up to half of their pupils by ability. They said 11-plus exams would deny places to pupils living near by and harm other schools by "creaming off" the brightest children.
Yesterday they won the agreement of Peter Downes, the schools adjudicator appointed to regulate new codes of practice on admissions. Mr Downes, a former headteacher, accepted the need for some partial selection to ensure a fully comprehensive intake at Burntwood School, Ernest Bevin College and Graveney School. But he ordered that only one in four applicants could be selected by ability.
In a separate ruling, plans to introduce part-selection at two schools in Croydon were rejected. Decisions due in the next few weeks could further erode partial selection, introduced by the Conservatives to allow comprehensives to choose some pupils by ability.
Campaigners welcomed the decisions, and predicted they would provoke further objections from parents. Margaret Tulloch, executive secretary of the Campaign for State Education, said: "Nothing changes unless people complain. I hope local authorities will realise that they can also change things."
However, Malcolm Grimston, Conservative chairman of Wandsworth's education committee, said the decision was "a sop to old Labour" and would encourage parents to desert the borough and send their children to schools elsewhere.
He said: "The system we have demonstrably works. I thought we were supposed to be concentrating on standards rather than ideology, but I was wrong.
"All it took was a small group of parents to appeal to an unelected apparatchik and the system is changed. The only people who might benefit are a few rich middle-class parents who are able to afford to buy homes near these good schools. That will be at the expense of more able children from less well-off parents elsewhere in the borough, who will be denied a place."
He said the success of a "comprehensive system of secondary provision rather than a system of comprehensive schools" showed in the borough's results. Ten years ago, one in three of its school places was empty. Now schools were over-subscribed and GCSE success was improving faster than the national average.
The decisions come as anti-selection campaigners prepare for the first round of ballots on the future of the remaining 166 grammar schools.
Parents' groups are expected to petition next month for the first local ballots, which will decide the future of selective schools.